This invention is directed generally to a connector for flexible coaxial cable and, in particular, to an electrical connector for terminating the end of flexible coaxial cable that is relatively small in size, that does not require any crimping and which has increased pull strength and improved anti-rotational captivation.
Coaxial connectors have taken many forms in the prior art as exemplified by U.S. Pat. No. 4,408,821 (Forney, Jr.) which is directed to a connector for semi-rigid coaxial cable. The connector for semi-rigid coaxial cable of Forney, Jr. is directed to a connector that does not require crimping. It uses a grip ring having multiple spline fingers extending therefrom and grooves on its inner surface, and a bored tubular shell member having a contoured internal diameter to accept the cable and the grip ring. When the grip ring and cable are inserted into the tubular body, the spline fingers resiliently deflect inwardly along the shell member contour, and embed into the outer semi-rigid cable sheath. The connector system can not provide termination for flexible cables because they do not include a semi-rigid sheath for the spline fingers to embed into.
U.S. Pat. No. 5,186,655 (Glenday, et al.) is directed to an RF connector. This connector locks in place by having a sleeve that is insertable between the outer conductor of a coaxial cable and the inner dielectric, such that the jacket and the outer conductor are deformed. After the sleeve is inserted, a coupling nut is then moved into place and frictionally engages the sleeve. This invention suffers deficiencies in the manner that the jacket electronically connects with the outer conductor, and the way that the coupling nut is coupled to the sleeve. The Glenday, et al. invention can not provide electrical performance for microwave frequencies because the method of deforming the plastic jacket on the outer conductor does not provide sufficient electrical contact at microwave frequencies. Therefore, this connector can not be used for microwave transmission, and is useful only for frequencies up to a few hundred MHz (CATV).
U.S. Pat. No. 5,607,325, incorporated herein by reference, describes an electrical connector for terminating flexible coaxial cable. The flexible cable includes an inner conductor, an intermediate dielectric, an outer flexible braided conductor and an outer insulator. A bored interface body has a first end with a first bore of relatively large inner diameter, a second end with a second bore of relatively smaller inner diameter than the first bore, and a third bore located therebetween of relatively smaller inner diameter than the second bore. A coupling member is located proximate to the interface body. An annular locking member having an inner diameter sized to receive the coaxial cable therein, an outer diameter sized to fit tightly within the first bore of the interface body, a first end having a collar and a second end having a plurality of ribs disposed proximate thereto is provided. This configuration allows for insertion of the second end of the locking member within the first bore of the interface body, so that the ribs of the locking member frictionally engage the inner wall of the first bore to lock the locking member to the interface body.
A typical connector for flexible microwave coaxial cable uses a ferrule to captivate the connector body to the cable jacket by friction. This crimp attachment improves the pull strength and anti-rotational (torque) captivation. Torque creates a potential failure for an coaxial cable assembly. Captivation of the cable jacket to the connector body is critical for many applications. Even highly flexible coaxial cable assemblies cannot withstand a large amount of torque. Pull strength is important for the mechanical integrity of a cable assembly. Additionally, the electrical performance of the cable assembly relies on mechanical captivation, particularly at high frequencies. Axial force applied to the cable can change the connector dimensions in the interface area, i.e., the contact and dielectric positions relative to the reference plane of the connector. This difference is small, usually about one or two millinches. It does not make a significant difference in the electrical performance of connector at the low frequencies; however, at frequencies higher than 18 GHz, the dimensional difference in the connector interface area has a crucial effect on electrical performance. Modern telecommunications systems need extended frequencies due to the high volume of information that is transmitted. Internet, Wireless, Space and Defense systems are growing at an exponential rate, creating great demands for more bandwidth.
The operational frequency limit of today""s typical coaxial assemblies is very high compared to the requirements of only a few years ago. Today, millimeter wave components (frequencies higher than 30 GHz) are common in the marketplace. Some manufacturers have 40 GHz coaxial cables in stock. Currently the highest operational frequency of a flexible coaxial assembly is approximately 65 GHz. In the near future, this limit is expected to extend up to 100 GHz.
For high frequency assemblies, the milliinch difference in the interface dimensions is significant, making the pull strength captivation very important. The best mechanical captivation and electrical performance method is a solder/crimp connector attachment, as shown in FIG. 1. The connector attachment is defined by a connector 210 which includes a connector or interface body 218 and a coaxial cable 232 formed with an outer insulator or jacket 224, an outer braided conductor 226, an inner insulator (not shown), and an inner conductor 230. Connector body 218 is substantially annular and includes a first end 270 and a second end 272. First end 270 is proximate a first annular body section 274 and second end 272 is located proximate a second annular body section 276 having a longer external diameter than first body section 274. Connector 210 also includes an annular extending crimped ferrule 278. As shown, outer conductor 226 is soldered to connector 218 by means of solder material 225. Outer conductor 226 is crimped, as shown at 279, in order to capture first body section 274 of connector body 218.
A connector with a crimp ferrule has fair axial and anti-torque captivation, but the crimp ferrule adds significant length. Soldering the cable outer conductor to the connector body provides a rigid bond between the connector body and the cable, but the solder joint is subject to cracking during vibration, flexure or thermal cycling, which may cause electrical and/or mechanical failure of the cable assembly. The soldering process also subjects the cable dielectric to excessive heat, which may cause the dielectric to expand, requiring retrimming of the interface dimensions. Crimp and solder crimp attachments have approximately the same length. The connector of U.S. Pat. No. 5,607,325, discussed above, is short in length, which is very convenient for customers. However, it cannot handle the high pull force that some customers require (sometimes more than 20 pounds without any electrical degradation) and it has limited anti-rotational captivation (typically only xc2x115xc2x0 for one cycle).
Accordingly, it is desirable to provide a connector for flexible coaxial cable that provides improved pull strength and improved anti-rotational captivation.
Generally speaking, in accordance with the present invention, an electrical connector for terminating flexible coaxial cable is provided. The connector includes a bored interface body having a first end with a first bore of relatively large inner diameter, a second end with a second bore of relatively smaller inner diameter than the first bore, and a third bore located therebetween of relatively smaller inner diameter than the second bore. A coupling member is located proximate the interface body and an annular locking member having an inner diameter sized to receive the coaxial cable therein is provided. The locking member having an inner diameter sized to receive the coaxial cable therein is provided. The locking member has an outer diameter sized to fit tightly within the first bore of the interface body, a first end having a collar and a second end having a plurality of ribs disposed proximate thereto, so that upon insertion of the second end of the locking member within the first bore of the interface body, the ribs frictionally engage the inner wall of the first bore to lock the locking member to the interface body.
Accordingly, by inserting the locking member within the interface body, a single coupling is formed. The coupling member is rotatably coupled to the interface body between the collar of the locking member and an enlarged portion of the interface body.
The flexible coaxial cable includes an inner conductor, an intermediate dielectric, an outer flexible braided conductor and an outer insulator. The outer insulator is stripped away from the end of the connector, and the outer flexible braided conductor is fanned-out, so that when the locking member is inserted into the interface body, the second end of the locking member bears against the fanned-out flexible conductor and pushes it against an internal wall of the interface body to thereby lock the coaxial cable to the interface body.
Preferably, the outer insulator of the coaxial cable is pre-conditioned for bonding to the locking member. As a result, pull strength is increased to 30 to 40 pounds and anti-rotational captivation is improved to xc2x190xc2x0 for multiple cycles. Furthermore, bonding of the cable to the locking member prevents moisture from migrating to the junction therebetween, thus extending the temperature range in which the cable can be used to between xe2x88x9255xc2x0 C. and +125xc2x0 C.
It is an object of the present invention to provide a connector for flexible coaxial cable that has a small profile and does not require crimping.
Another object of the present invention is to provide a connector for flexible coaxial cable that provides a transmission medium from direct current to millimeter waves.
Yet another object of the present invention is to provide flexible coaxial cable that provides the electrical product designer with maximum flexibility.
A further object of the present invention is to provide a connector for coaxial cable that does not require soldering of the outer conductor which may cause dielectric damage; however, the center conductor should be soldered.
Still another object of the invention is to provide a coaxial cable with a profile that is lower than the standard right angle connectors designed for flexible coaxial cable.
Yet a further object of the invention is to provide a connector for flexible coaxial cable having improved pull strength and improved anti-rotational captivation.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.
Accordingly, the invention comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.